Material having electric permittivity and magnetic permeability that are simultaneously negative at certain frequencies have a negative index of refraction for these frequencies. Plasmonic ring resonators (PRRs), which include split ring resonators (SRRs), have been used to create materials having a negative index of refraction, also termed negative index materials (NIMs). See, for example, commonly-owned U.S. Pat. Nos. 7,646,524, 7,683,444, and 7,808,722 as well as Fast Light, Slow Light and Left-Handed Light, P. W. Milonni, Institute of Physics Publishing (2005), each of which is incorporated herein by reference in its entirety.
NIMs have several applications, for example in the production of superlenses, which overcome the diffraction limit by enhancing and recovering the evanescent waves emitted by an object to allow resolution of features much smaller than the incident wave. Although NIMs have been produced in the microwave frequencies, it remains a challenge to produce NIMs that operate in the visible/near infrared spectrum due to the required size of the resonant structures. Moreover, it has been proposed that, in theory, a ring of metallic nanoparticles can create magnetic oscillations at optical frequencies by the formation of displacement currents excited from an optical source. Such optically active structures can produce a permeability value different from unity at optical and near infrared frequencies.
The various structures necessary for realizing such optical phenomena require nanoscopic control of structural details. Nano-lithographic techniques to create such structures with features in the range of 10 or 10s of nanometers are time consuming, expensive and suffer from a lack of registration over extended length scales. Thus, a need exists for fabrication of high resolution nanoscale metamaterial structures.